Method for optimizing exchanges of information on acknowledgement in asynchronous communication between terminal and network

ABSTRACT

In a method for optimizing exchanges of acknowledgement signals between a mobile equipment in asynchronous communication with a plurality of base stations of a cellular telecommunication network, the terminal sends data to the base stations and each base station is likely to return to the terminal a positive acknowledgement ACK or negative acknowledgement NACK. The method includes the steps of: synchronizing the mobile equipment with the network; and estimating quality of downlink communication between each base station and the mobile equipment on at least one standardized channel, such that if at least one base station returns an acknowledgement to the mobile equipment, the mobile equipment only requests a NACK from the base stations whilst the data is continuously being transmitted, and if all the base stations return a NACK to the mobile equipment, the mobile equipment only requests an ACK from the base stations during the current communication.

TECHNICAL FIELD

The present invention is located in a field of telecommunications, andmore specifically relates to the method for optimizing exchanges ofacknowledgement signals between a mobile equipment such as a mobileterminal in asynchronous communication with a plurality of base stationsof a cellular telecommunication network during which the mobileequipment sends data to the base stations and each base station is ableto return a positive acknowledgement ACK to the mobile equipment if thisbase station receives correctly the data transmitted by the mobileequipment, or a negative acknowledgement NACK if it does not receivecorrectly the data transmitted by the mobile equipment.

The present invention also relates to mobile equipment capable oftransmitting data to a plurality of base stations of a cellulartelecommunication network and for receiving a positive acknowledgementACK from a base station, if the data was all correctly received by thebase station, or a negative acknowledgement NACK if the data wasincorrectly received by the base station.

BACKGROUND ART

To allow mobile terminals to perform a high speed communication viacellular communication networks, the specifications of the group 3GPP(Third generation partnership project) adopt an architecture similar tothat of the service HSDPA (High Speed Downlink Packet Access) to providethroughputs up to 2 Mbps (megabits per second) via an EUDCH (EnhancedUplink Dedicated Channel) uplink channel or HSUPA (High Speed UplinkPacket Access) for future multimedia applications in UMTS (UniversalMobile Telecommunications System). In order to automatically controlacknowledgement signaling between terminals and base stations, thespecifications of the group 3GPP provide to add a supplementary protocollayer HARQ (Hybrid Automatic Request), at the level of the MAC (MediaAccess Control) sub-layer of layer 2 of the radio interface protocols.

The new protocol layer HARQ is provided to allow the base stations ofthe network to transmit positive acknowledgement signals ACK to theterminal if all the packets transmitted by the terminal are correctlyreceived by base stations or a negative acknowledgement sign signal NACKif all the packets transmitted by the terminal are not correctlyreceived by base stations. In case of a transmission fault, then theterminal has to coordinate itself with the network in order tore-transmit the packets.

Moreover, these specifications of the group of 3GPP provide that all thecells involved in a communication with the terminal send explicitly apositive acknowledgement ACK if the transmission is correct, whichincreases interferences at terminal level. In addition, as far as thenumber of NACK is about from 10% to 20% and the number of ACK represents90%, it would be advantageous to provide a mechanism allowing basestations to get rid of emitting ACKs to the terminal when it is possibleto deduce implicitly that the data were received.

In case of a synchronous communication in which a terminal and a networkexpect to receive data during a predetermined time TTI (TransmissionTime Interval), exchanges of acknowledgement are optimized by the methoddescribed in French patent application No. 0550910 filed on the same dayby the applicant and titled “procédé d'optimisation des échangesd'information d'accusé de réception dans une communication synchroneentre un terminal et un réseau (method for optimizing exchanges ofinformation on acknowledgement in synchronous communication between aterminal and a network)”.

In case of an asynchronous communication, base stations of a network donot expect to receive data during a predetermined time, and thereforewill not be able to transmit to the terminal an acknowledgementindicating that the data was not received in case of a radio linkageproblem between the terminal and the network. Then the terminalcontinues transmitting the data needlessly while they are not correctlyreceived by the network.

DISCLOSURE OF THE INVENTION

A first object of the present invention is to allow base stations todetect a transmission error in an asynchronous communication.

A second object of the invention is to reduce the number ofacknowledgement signals transmitted to mobile equipment such as a mobileterminal by base stations of a network.

Another object of the invention is to allow mobile equipment such as amobile terminal to determine the type of acknowledgement that it needsfrom the analysis of its proper radio conditions.

These objects are achieved by means of a method for optimizing exchangesof acknowledgement signals between a mobile equipment in asynchronouscommunication with a plurality of base stations of a cellulartelecommunication network during which the mobile equipment sends datato the base stations and each base station is likely to return apositive acknowledgement ACK to the mobile equipment if the base stationreceives the data transmitted by the mobile equipment correctly, or anegative acknowledgement NACK if the data transmitted by the mobileequipment was incorrectly received by the base stations.

The method according to the invention comprises the following steps of:

synchronizing the mobile equipment with the network; and

estimating quality of downlink communication between each base stationand the mobile equipment on at least one standardized channel, such thatif at least one base station returns an acknowledgement to the mobileequipment, the mobile equipment only requests a negative acknowledgementNACK from the base stations whilst the data is continuously beingtransmitted, and if all the base stations return a negativeacknowledgement NACK to the mobile equipment, the mobile equipment onlyrequests a positive acknowledgement ACK from the base stations duringthe current communication.

According to the invention, if at least one base station returns apositive acknowledgement ACK to the terminal (i.e., the mobileequipment), the terminal requires only a negative acknowledgement NACKfrom the base stations during a current communication and, if all basestations return a negative acknowledgement NACK to the terminal, theterminal requires only a positive acknowledgement ACK from the basestations while data is continuously transmitted.

In a first variation of implementation of the method according to thepresent invention, the mobile equipment re-transmits the data only ifestimated quality of all the channels is less than a predeterminedvalue.

In a second variation, the mobile equipment re-transmits the data onlyif the estimated quality of at least one channel is less than apredetermined value and is all the other base stations send a negativeacknowledgement NACK to the mobile equipment.

The invention is implemented by a mobile equipment such as for example aGSM (Global System for Mobile Communications) or UMTS telephone, capableof transmitting data to a plurality of base stations of a cellulartelecommunication network and of receiving a positive acknowledgementACK from a base station, if the data was correctly received by the basestation, or a negative acknowledgement NACK, if the data was incorrectlyreceived by the base station.

This mobile equipment includes:

means for estimating quality of downlink communication of each basestation of the network on at least one standardized channel; and

decision making means for either only requesting a negativeacknowledgement NACK or only a positive acknowledgement ACK from thebase stations depending on the quality of the estimated communicationchannel.

The present invention allows optimizing exchanges of the acknowledgementsignals ACK and NACK between the mobile equipment and the base stations,thus reducing the interferences at mobile equipment level.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view illustrating a synchronizing phase of aterminal with a network;

FIG. 2 is a schematic view illustrating a first situation in a networkin which the method according to the present invention is implemented;

FIG. 3 is a schematic view illustrating a second situation in thenetwork in which the method according to the present invention isimplemented;

FIG. 4 is a schematic view illustrating a third situation in the networkin which the method according to the present invention is implemented;and

FIG. 5 is a block diagram illustrating an example of a mobile terminalaccording to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

The following description relates to an implementation of the presentinvention in a network based on the WCDMA (wideband code divisionmultiple access) technology. More precisely, the invention will bedescribed in a UMTS network.

-   -   In UMTS, the radio interface contains three main layers:    -   the physical layer (layer 1),    -   the data link layer (layer 2) and    -   the radio resource control (RRC) layer.

Layer 2 is composed of four sub-layers:

-   -   the MAC (Media Access Control) sub-layer,    -   the RLC (Radio Link) sub-layer,    -   the PDCP (Packet Data Convergence Protocol) sub-layer and    -   the BMC (Broadcast/Multicast Protocol) sub-layer.

The new protocol layer HARQ intended to control acknowledgementsignaling between base stations and terminals is provided at MACsub-layer level.

In UMTS, the network transmits permanently to a terminal in a currentcell a primary code and a second code of synchronization respectivelyvia a primary channel PSCH (Primary Synchronization Channel) and asecondary channel SSCH (Secondary Synchronization Channel) foridentifying the neighboring UMTS cells, as well as a beacon channelcalled CPICH (Common Pilot Channel) for estimating pulse response of thepropagation channel. The CPICH channel is composed of a predefinedsequence of bits/symbols (so-called pilot) which are permanentlytransmitted over the cells. Throughput of these bits/symbols is constantand equal to 30 kbps (kilobits per second), that is 15 ksps(kilo-symbols per second). The CPICH channel is not associated withtransportation channel. Contrary to a synchronous communication in whichthe base stations and the terminal know that during a TTI time(Transmission Time Interval) a transportation block will be exchanged,in an asynchronous communication, the base stations of the network donot know the timing at which the terminal starts transmitting the data.Also, a first phase of the method consists in synchronizing the terminaland the network.

FIG. 1 illustrates schematically the synchronizing phase of a mobileterminal MS and a base station BS of the network.

At step 10, the terminal MS sends to the base station BS the datapackets accompanied with a request in which the terminal asks to thebase stations to return to it a positive acknowledgement ACK at the endof a predetermined time D. If the terminal does not receive the ACKsignal from the network (step 12), the terminal returns (step 14) thedata and the request and estimates the quality of the link from thepulse response of the propagating channel measured in the CPICH channel.Upon receiving a positive acknowledgement ACK from at least one basestation (step 16), the terminal returns (step 18) the data accompaniedwith a request in which the terminal asks to the base stations to onlysend negative acknowledgements NACK as far as the estimated quality ofthe link is higher than a predefined quality.

FIG. 2 illustrates schematically mobile terminal 20 in asynchronouscommunication with three base stations 22, 24 and 26 of the network. Inthe communication illustrated in FIG. 2, all the base stations receivedcorrectly the data transmitted by terminal 20.

In reference to FIG. 2A, after the synchronizing phase, terminal 20sends (arrow 30) data packets to base stations 22, 24 and 26 andreceives at the same time pilot bits/symbols from each of the basestations (arrow 32) via the CPICH channel.

In FIG. 2B, during the waiting time D of acknowledgement signals,terminal 20 determines power of the signals received from each basestation 22, 24, 26 from the analysis of the bits/symbols transmitted viathe CPICH channel, and compares the measured powers with a predeterminedthreshold power. If the power measured for each base station is higherthan the threshold value, the terminal deduces that the transmittedpackets were correctly received by base stations 22, 24 and 26 and sends(arrow 34, FIG. 2C) next packets without waiting for an ACK signal.Thanks to this mechanism, terminal 20 deduces an implicit ACK signalfrom the measurements made on the CPICH channel. Therefore, basestations 22, 24 and 26 are exempt from transmitting explicitly an ACKsignal to the terminal. This allows power saving on a downlink, whichcan be allocated to another function.

FIG. 3 illustrates schematically a second situation in which some basestations did not correctly receive the data transmitted by the terminal.

In reference to FIG. 3A, terminal 20 sends (arrow 30) data packets tobase stations 22, 24 and 26 and receives at the same time pilotbits/symbols from each station (arrow 32) via the CPICH channel. In thiscase, base station 22 sends a NACK signal (arrow 40, FIG. 3B) toterminal 20. During the waiting time of acknowledgement signals,terminal 20 determines power of the signals received from each basestation 22, 24, 26 from the analysis of the bits/symbols transmitted viathe CPICH channel and compares the measured powers with thepredetermined threshold power. If the power measured for each basestation is higher than the threshold value, the decision modulecontained in terminal 20 deduces that the packets sent by terminal 20were correctly received at least by base stations 24 and 26 and sends(arrow 42, FIG. 3C) next packets without waiting for an ACK signal andwithout taking into account the NACK signal (arrow 40) emitted by basestation 22. Base stations 22, 24 and 26 continue sending (arrow 32)bits/symbols to the terminal via the CPICH channel.

The method according to the invention allows us to take intoconsideration in this case an attenuation of the signal emitted by basestation 22 due physical conditions of transmission and to avoidretransmission of packets insofar as other base stations receivedcorrectly the packets emitted by the terminal.

FIG. 4 illustrates schematically a third situation in which no basestation received correctly the data transmitted by the terminal.

In reference to FIG. 4A, terminal 20 sends (arrow 30) data packets tobase stations 22, 24 and 26 and receives at the same time pilotbits/symbols from each base station (arrow 32) via the CPICH channel. Inthis case, two base stations 22 and 24 send a NACK signal to terminal 20(arrows 50 and 52, FIG. 4B). During the waiting time of acknowledgementsignals, terminal 20 determines power of the signals received from eachbase station 22, 24, and 26 from the analysis of the bits/symbolstransmitted via the CPICH channel and compares the measured powers witha predetermined threshold power. In this case, if the measured power ofthe signal received (arrow 54) from base station 26 is lower than thethreshold value, the terminal deduces that none of base stations 22, 24or 26 correctly received the packets sent by terminal 20. Terminal 20returns (FIG. 4C) the same packets to the base stations (arrow 60) andcarries out again measures on the signals transmitted by the basestations (arrow 32) via the CPICH channel. This operation will berepeated until at least one of base stations 22, 24 or 26 receivescorrectly the packets emitted by terminal 20.

An example of the constitution of terminal 20 is illustrated in FIG. 5.Terminal 20 has antenna 70 for communicating with the base stations overthe air, transmitter circuit 72 connected to antenna 70, receivercircuit 74 connected to antenna 70, estimation module 76, decisionmodule 78, and control module 80. Estimation module 76 is connected toreceiver circuit 74, and arranged for estimating quality of downlinkcommunication from each base station on the CPICH channel. Specifically,estimation module 76 receives the pilot bits/symbols transmitted via theCPICH channel from receiver circuit 74, analyzes the pilot bits/symbols,and measures the power of reception signals from the result of theanalysis. Decision module 78 receives the measured power from estimationmodule 76, and makes the decision whether terminal 20 requests only anegative acknowledgement NACK or requests only a positiveacknowledgement ACK from the base stations depending on the measuredpower. Control module 80 is provided for managing the synchronizationprocess of terminal 20 with the network, and for controlling theexchanges of data packets and acknowledgement signals between terminal20 and the base stations as described above in accordance with theresult of decision in decision module 78.

The invention allows optimizing exchanges of the signals ACK and NACKbetween the terminal and the network, thus reducing the interferences atterminal level.

1. A method for optimizing exchanges of acknowledgement signals betweena mobile equipment in asynchronous communication with a plurality ofbase stations of a cellular telecommunication network by synchronizingsaid mobile equipment with the cellular telecommunication network, saidmobile equipment sends data to said base stations and each base stationis configured to return a positive acknowledgement ACK to the mobileequipment if the base station receives the data transmitted by themobile equipment correctly, or a negative acknowledgement NACK if thedata transmitted by the mobile equipment was incorrectly received bysaid base stations, the method comprising the steps of: estimatingquality of downlink communication between each base station and themobile equipment on at least one channel, such that if at least one basestation returns an acknowledgement to the mobile equipment, said mobileequipment only requests a negative acknowledgement NACK from said basestations for all subsequent data transmission while said estimatedquality is higher than a preset value; transmitting the data with anrequest for a base station to respond with a positive acknowledgementACK or a negative acknowledgement NACK within a predetermined period oftime and wherein said estimating the quality of downlink communicationoccurs if said positive acknowledgment ACK or said negativeacknowledgment NACK is not received within said predetermined period oftime; and re-transmitting said data only if the estimated quality of theat least one channel is less than the preset value for each base stationor if the estimated quality of at least one channel from at least onebase station is less than the preset value and all the other basestations send a negative acknowledgement NACK to the mobile equipment.2. The method according to claim 1, wherein said network is a networkbased on WCDMA (Wide Code Division Multiple Access) technology.
 3. Themethod according to claim 2, wherein said network is a UMTS (UniversalMobile Telecommunications System) network.
 4. The method according toclaim 3, wherein said channel is a CPICH (Common Pilot Channel) channel.5. Mobile equipment capable of transmitting data to a plurality of basestations of a cellular telecommunication network and of receiving apositive acknowledgement ACK from a base station, if the data wascorrectly received by said base station, or a negative acknowledgementNACK, if the data was incorrectly received by said base station, themobile equipment comprising: means for estimating quality of downlinkcommunication of each base station of the network on at least onechannel; decision making means for either only requesting a negativeacknowledgement NACK or only a positive acknowledgement ACK from saidbase stations depending on the quality of said estimated communicationchannel; means for transmitting the data with an request for a basestation to respond with a positive acknowledgement ACK or a negativeacknowledgement NACK within a predetermined period of time and whereinsaid means for estimating the quality of downlink communicationestimates the quality if said positive acknowledgment ACK or saidnegative acknowledgment NACK is not received within said predeterminedperiod of time; and means for re-transmitting said data only if theestimated quality of the at least one channel is less than the presetvalue for each base station or if the estimated quality of at least onechannel from at least one base station is less than the preset value andall the other base stations send a negative acknowledgement NACK to themobile equipment.
 6. The mobile equipment of claim 5, wherein saidnetwork is a network based on WCDMA (Wide Code Division Multiple Access)technology.
 7. The mobile equipment of claim 5, wherein said network isa UMTS (Universal Mobile Telecommunications System) network.
 8. Themobile equipment of claim 5, wherein said channel is a CPICH (CommonPilot Channel) channel.
 9. The method according to claim 1, wherein ifsaid positive acknowledgment ACK or said negative acknowledgment NACK isnot received within said predetermined period of time and if saidestimated quality for said at least one channel is higher than thepreset value for at least one base station, said mobile equipmenttransmits new data to said base stations without waiting for anacknowledgement.